The present invention relates to the real time allocation of control authority among the control effectors of a controllable vehicle in executing a commanded maneuver, such allocation being made in consideration of the possible nonlinear and non-monotonic effects the displacement of those control effectors may produce on the vehicle and on each other in affecting such maneuver. The invention is explained in terms of its application to aircraft; however, the invention is equally applicable to any air, space, sea, under-sea, or ground vehicle, whose dynamics are controllable via selected set of control effectors.
The in-flight control and maneuvering of aerodynamic vehicles, such as aircraft, are accomplished by positioning the aircraft's control surfaces to modify the airflow across them to affect an aerodynamic response from the aircraft. The control surfaces, along with other force and moment producing devices such as thrust vectoring, are referred to as “control effectors” The control effectors are position controlled by the aircraft's flight control system in response to pilot (or auto-pilot) commands to maintain or alter the aircraft's position using roll, pitch and yaw maneuvers, or direct force such as direct lift. With legacy aircraft, the principal control surfaces are the ailerons (roll), elevators (pitch), and rudders (yaw).
Today, however, with the evolution of aircraft design to include tailless airplanes, such as the delta wing fighter plane with its requirement for high agility and low profile that limits vertical control surfaces, advanced control concepts are required to replace the vertical tail and rudder control surfaces. New aircraft designs, whether necessary to meet military requirements or to achieve improved fuel efficiencies for commercial and private aircraft, have included an increased number of control effectors. The increased number provides both redundancy for flight safety in the event of a control effector failure, as well as offering the aircraft flight control system a greater suite of effectors that may be used collectively to optimize the vehicle's aerodynamic performance and stability. Advanced control laws are then required to utilize this larger control effector suite to maximize the performance capabilities of the vehicle.
The control effectors are each driven by their associated actuator, or by pairs of actuators when redundancy is required for fail safe operation. The effectors are positioned and repositioned as necessary to supplement or supplant the aerodynamic affects produced by the legacy control surfaces to achieve the commanded flight maneuver or condition. With differences in the aerodynamics required by different maneuvers and the different effects that each control effector is designed to produce, the flight control system must allocate execution of the commanded maneuver among several control effectors. The allocation is determined by the type of commanded action, the current flight conditions, and the known response characteristics of the aircraft. The flight control system determines the control actions, i.e. the forces, moments, rotational accelerations, and/or linear accelerations required from the control effector suite in each of the vehicle's control axes to execute a given maneuver. These forces, moments, rotational accelerations, and/or linear accelerations define reference commands to the control allocation algorithm which determines the individual control effector commands required for the control effector suite to produce responses that track the reference commands.
Each control effector's authority in executing the command is then determined using a control allocation algorithm, and the effector is held in its commanded position through set point control of its actuator(s). The prior art flight control systems, however, use control allocation algorithms which assume linearity of the control effector effects and use techniques, such as a pseudo-inverse to generate the actuator commands. This does not account for the possibility of interactions between control effectors whose response is nonlinear, and which may exhibit significant interactions between them. Those known control methods which do assume control effector nonlinear and non-monotonic interactions use iterative techniques, such as linear programming to account for these interactions. These iterative solution techniques make them undesirable for embedded software applications.